1. Field of the Invention
The invention relates to an emission controlling device suitably used in automobiles powered by an internal combustion engine. More particularly, the invention relates to a device for treating exhaust gases of internal combustion engines and still more particularly to the thermal shielding of a catalytic converter.
2. Description of Related Art
A conventional device for treating exhaust gases of internal combustion engines, such as a catalytic converter, includes a housing connected to an inlet conduit and an outlet conduit. The housing contains at least one exhaust gas treating body, commonly known as a substrate. The substrate is typically a monolith that possess hundreds or thousands of channels arranged in a honeycomb structure, which serve as exhaust channels through which exhaust gas from the engine flows from an inlet conduit and to an outlet conduit.
The monolith is typically ceramic, but it can also be composed of metal. Substrates are also often coated with an active catalytic layer such as aluminum oxide, platinum, palladium, and/or rhodium. As the exhaust flows through the substrate(s), it interacts with the active catalysts and chemical reactions reduce the pollutants in the exhaust, such as carbon monoxide (CO), hydrocarbons (HCs), and nitrogen oxides (NO or NO2).
Catalytic converters also often include a system to monitor the oxygen level in the exhaust. A sensor located in the catalytic converter measures the oxygen level in the exhaust, and determines whether or not the exhaust system is operating properly and emissions are within acceptable limits.
The exhaust flowing through the catalytic converter is extremely hot (exhaust temperatures may be as high as 1900 degrees Fahrenheit). Excessive housing temperatures potentially pose a danger to the automobile itself and the environment, potentially causing undesired thermal incidents. Therefore, catalytic converters often contain insulation and/or shielding to reduce the housing temperature or exposure of other components.
Catalytic converters are known to possess internal shields welded to the housing inner surface for certain applications. However, it is difficult to successfully weld a shield to the housing, when the outer housing is one solid piece instead of two pieces connected together. Additionally, insulation material can interfere with the welding process.
Also known are catalytic converters with internal shields installed in the housing by the process of forming the housing. During forming, the internal shield is positioned in its desired location, and part of the housing is deformed such that the cross-sectional contour of the housing is not uniform in the axial direction in the area proximal to the internal shield. This deformation prevents the internal shield from moving in the axial direction of the catalytic converter. One disadvantage to forming is that the sensor, sensor boss, housing opening, internal shield, or other components may be damaged during the process. This problem is especially prevalent where the sensor is located along the area proximal to the internal shield.
The prior art further discloses a catalytic converter with one continuous piece of insulation surrounding the substrate(s) and the internal shield. Using one piece of insulation may cause problems during manufacturing because it may require the manufacturer to insert all of the elements (the insulation, the substrate(s), and the internal shield) into the housing all at once. Additionally, it is more difficult to achieve a tight interference fit for both the coupling between the shield and insulation and the coupling between the substrate(s) and insulation if the same insulation is used for both applications.
In view of the above, it is clear that an emission control device housing with a uniform cross-sectional contour in the axial direction in the area proximal to the internal shield would be advantageous. Additionally, insulation that does not require the manufacturer to simultaneously install many elements into the housing would be advantageous.